Geographic Range

New Zealand mudsnails (Potamopyrgus antipodarum) are native to freshwater streams and lakes of New Zealand and small, neighboring islands. However, by several speculated means of human introduction, they have become an invasive species in Australia, Europe, and North America. Occurrences of the species in North America, most of which are in the western United States, have been carefully documented since it was first discovered in Idaho. The snails are known to be established in Oregon, California, northern Arizona, New York, and Canada, affecting major freshwater systems such as Lake Ontario, Lake Erie, and Lake Superior. They also have been recently introduced in Japan. (Alonso and Castro-Díez, 2008; Benson and Kipp, 2009)

Habitat

New Zealand mudsnails prefer to live in streams and the littoral zones of lakes. They prefer shallow areas but can be found up to 60 m deep. They can be found in aquatic habitats of varying substrate types, including silt, sand, gravel, cobble, and macrophyte/vegetation. Densities are highest in macrophyte habitats and lowest in silt/sand habitats. Individuals of this species live in both eutrophic and clear waters, but they thrive in disturbed or degraded waters. New Zealand mudsnails can tolerate a wide range of temperatures, from near freezing to 34ºC. The optimal salinity of the water for the snails is near 5%, but they can tolerate brackish waters and even survive salinities as high as 30 to 35% for short periods of time. New Zealand mudsnails prefer low water velocities but can be found in high velocity areas buried in the sediment or underneath cobbles and boulders. ("Monitoring the aquatic food base in the Colorado River, Arizona during June and October 2002: Annual report", 2003; Benson and Kipp, 2009; Gustafson, et al., 2004; Richards, 2002)

Physical Description

New Zealand mudsnails are shelled organisms that are either gray in color or some shade of light to dark brown. Male and female New Zealand mudsnails are very similar in physical appearance, but females are distinguished from males by the presence of developing embryos in their reproductive systems. In the western United States, the average length of the shell of the New Zealand mudsnail is 4 to 5 mm, with a maximum length of 6 to 7 mm. In their native range, the maximum length of the shell is 12 mm. The surface of the shell is characterized by right-handed coiling of 5 to 6 whorls demarcated by sulci. The shells of some individuals have a keel in the middle of each whorl and/or spines for defense against predators. A terminal oval aperture covered by a thin operculum is also present. New Zealand mudsnails may resemble snails native to the United States, but they are distinguished by their longer, narrower shells that have a greater number of whorls. (Alonso and Castro-Díez, 2008; Benson and Kipp, 2009; Crosier and Molloy, 2010)

Development

New Zealand mudsnails are ovoviviparous, meaning that the development of embryos in their eggs actually occurs within the female. After completing development, the eggs hatch within the female, and the female then gives birth to the young snails. New Zealand mudsnails have been observed to grow 0.1 mm/day at 21ºC under laboratory conditions, with growth rates depending on the size of the individual. Females reach maturity at 3 to 6 months of age. (Crosier and Molloy, 2010; Gustafson, et al., 2004)

Reproduction

New Zealand mudsnails are dioecious. Populations in New Zealand consist of sexual males and both sexual and asexual females, whereas introduced populations are comprised entirely of asexual females.

In their native range, individuals that reproduce sexually are promiscuous. During copulation, the male is found on top of the shell of a female, and the apertures of the two snails are in contact. Females can either maintain their position and proceed with mating or move in a manner that displaces the males. The duration of copulation is typically between 20 minutes and 1.5 hours. Males do not discriminate between sexual females and asexual or parasitically-castrated females, although their genes will not be passed to the offspring of the latter two types of females.

Populations found in the United States consist of triploid females that reproduce asexually by way of parthenogenesis. This type of asexual reproduction is also observed in their native range and leads to populations of genetically identical females or clones in both their native and introduced habitats. (Benson and Kipp, 2009; Crosier and Molloy, 2010; Neiman and Lively, 2004)

In New Zealand, reproduction typically occurs every three months. In the western United Staes, reproduction occurs throughout the year, with seasonal peaks during the months of March and October. Females reach sexual maturity at a shell length of 3 mm and produce approximately 230 young per year. Larger females produce more offspring than smaller females, and asexual females produce double the number of female offspring produced by sexual females. This species is ovoviviparous, carrying as many as 10 to 120 eggs at a time for development and giving birth to live snails. Developing embryos are sometimes present within the reproductive system of asexual females at the time of birth. (Benson and Kipp, 2009; Crosier and Molloy, 2010; Gustafson, et al., 2004)

Lifespan/Longevity

Under laboratory conditions, marked individuals were observed to survive over one year. The lifespan of New Zealand mudsnails in natural conditions is unknown. (Gustafson, et al., 2004)

Range lifespanStatus: captivity

1 (high) years

Behavior

New Zealand mudsnails exhibit positive rheotactic behavior -- they tend to crawl against the current in flowing water. One authority estimated substrate cruising speed at greater than one meter per hour, pretty fast for a snail. They also float, alone and in mats of algae such as Cladophora. During unfavorable environmental conditions, such as dry or cold periods, individuals of this species are observed to bury into the substrate. (Alonso and Castro-Díez, 2008; Benson and Kipp, 2009; Gustafson, et al., 2004)

New Zealand mudsnails are reported to be nocturnal grazers, although non-brooding females and juveniles foraging more during the day. It is believed that non-brooding females and juveniles behave in this way that risks predation in order to obtain the necessary energy required for reproduction and growth, respectively. Infection by trematode parasites of the genus Microphallus alters the foraging behavior of the snails, causing them to forage more during the morning hours when ducks, the predators of New Zealand mudsnails and the final hosts of Microphallus, are foraging. This change in foraging time increases the likelihood of parasite transmission. (Benson and Kipp, 2009; Levri and Lively, 1996)

Home Range

Home range sizes for New Zealand mudnails are unknown.

Communication and Perception

Perception in New Zealand mudsnails is mainly via chemical cues. In their native range, the chemical odor of predatory fish causes the snails to hide under rocks in an attempt to evade predation. They are also able to sense light. (Benson and Kipp, 2009)

Food Habits

New Zealand mudsnails are considered scrapers/grazers. Their diet consists of diatoms, epiphytic and periphytic algae, and animal and plant detritus. Therefore, they can be considered planktivores, algivores, and detrivores. (Benson and Kipp, 2009)

Other Comments

Several aspects of the ecology of New Zealand mudsnails have contributed to their success as an invasive species. First, their tolerance of a wide range of abiotic conditions, such as temperature and salinity, aids them in transport from their native range via the ballast water of ships. Second, their escape from natural predators and parasites and their high competitive ability at the early stages of succession contribute to their establishment in introduced habitats. Third, their high fecundity, fast reproductive rate, and active and passive means of dispersal aid in their spread. Finally, their great abundance allows them to impact the ecosystem by consuming most of the primary production, dominating nutrient cycles and secondary production and decreasing populations of other mollusks and grazers. (Alonso and Castro-Díez, 2008)

The potential and realized negative impacts of New Zealand mudsnails have been recognized, and measures are being taken to control their spread based on what is known about their ecology. New Zealand mudsnails experience mortality when exposed to freezing or high temperatures with low humidity. It is recommended that all equipment that could be harboring the snails be frozen for several hours or be exposed to temperatures of 29 to 30ºC and low humidity for a minimum of 24 hours or temperatures greater than 40ºC and low humidity for a minimum of two hours. (Richards, et al., 2010)

Contributors

Alexa-Jade Simeron (author), The College of New Jersey, Keith Pecor (editor), The College of New Jersey, George Hammond (editor), Animal Diversity Web Staff.

Glossary

Australian

Living in Australia, New Zealand, Tasmania, New Guinea and associated islands.

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

Palearctic

living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.

asexual

reproduction that is not sexual; that is, reproduction that does not include recombining the genotypes of two parents

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

brackish water

areas with salty water, usually in coastal marshes and estuaries.

chemical

uses smells or other chemicals to communicate

detritivore

an animal that mainly eats decomposed plants and/or animals

detritus

particles of organic material from dead and decomposing organisms. Detritus is the result of the activity of decomposers (organisms that decompose organic material).

ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

female parental care

parental care is carried out by females

fertilization

union of egg and spermatozoan

freshwater

mainly lives in water that is not salty.

herbivore

An animal that eats mainly plants or parts of plants.

internal fertilization

fertilization takes place within the female's body

intertidal or littoral

the area of shoreline influenced mainly by the tides, between the highest and lowest reaches of the tide. An aquatic habitat.

introduced

referring to animal species that have been transported to and established populations in regions outside of their natural range, usually through human action.

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

nocturnal

active during the night

oceanic islands

islands that are not part of continental shelf areas, they are not, and have never been, connected to a continental land mass, most typically these are volcanic islands.

ovoviviparous

reproduction in which eggs develop within the maternal body without additional nourishment from the parent and hatch within the parent or immediately after laying.

the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.

seasonal breeding

breeding is confined to a particular season

sedentary

remains in the same area

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

solitary

lives alone

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

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The Animal Diversity Web is an educational resource written largely by and for college students. ADW doesn't cover all species in the world, nor does it include all the latest scientific information about organisms we describe. Though we edit our accounts for accuracy, we cannot guarantee all information in those accounts. While ADW staff and contributors provide references to books and websites that we believe are reputable, we cannot necessarily endorse the contents of references beyond our control.

This material is based upon work supported by the
National Science Foundation
Grants DRL 0089283, DRL 0628151, DUE 0633095, DRL 0918590, and DUE 1122742. Additional support has come from the Marisla Foundation, UM College of Literature, Science, and the Arts, Museum of Zoology, and Information and Technology Services.